Domestic appliances may have rotatable components whose rotation may give rise to unwanted, irregular motions, particularly in the form of unbalances. This applies, in particular, to rotatable components of domestic appliances which serve to rotate objects for the treatment of which the respective domestic appliance is provided. Examples of such rotatable components are drums of washing machines and washer-driers, and rotary equipment (e.g. rotary plates) in microwave ovens and kitchen stoves.
Unwanted motions resulting from unbalance of rotatable components may occur if, in particular, the mass of objects to be rotated or being rotated in or by means of rotatable components is distributed in a non-uniform manner. A particularly demonstrative example of this is a non-uniform distribution of washing in a drum of a washing machine, which non-uniform distribution, particularly at high rotational speeds of the drum (e.g. in spinning), may give rise to unbalances and, resulting therefrom, unwanted motions of the drum.
For the domain of washing machines, the practice of detecting the unbalance of the drum is known in the art. Known approaches use mass-and-spring systems, wherein motions caused by unbalance of the washing-machine drum are detected. In such cases, the resonant frequency of the mass-and-spring system is usually so set that the mass-and-spring system is brought into resonant vibration when motions of the washing-machine drum that are generated by unbalance attain a predefined quantity, cf. EP 0 750 065 A1. This approach, however, does not permit precise detection of unwanted motions of the washing-machine drum that result from unbalance, as would be desirable for an optimized control of the rotation of the washing-machine drum.
Furthermore, known approaches are disadvantageous in so far as they use elaborate systems or methods to deduce motions of the washing-machine drum from movements of the mass of the mass-and-spring system.
DE 199 20 870 A1 describes a washing machine which permits measurement of the weight of the washing. For this purpose, a pressure that is dependent on the weight of the washing is measured and converted into a weight. DE 100 07 839 A1 describes a vibration detector device having a coil whose core is movable by reason of vibration and thereby alters the inductance of the coil.